Pressure relief devices are commonly used as safety devices in systems containing pressurized fluids in gas or liquid form. A pressure relief device will vent fluid from a system when the pressure in the system reaches a predetermined level—usually before it reaches an unsafe level. Exemplary pressure relief devices include explosion vents and rupture disks. Examples of pressure relief devices include those illustrated in co-owned U.S. Pat. Nos. 4,441,350 and 4,481,850, the entire contents of which are hereby incorporated by reference.
Pressure relief devices may come in any number of materials and shapes. Pressure relief devices are commonly manufactured from metal; however, they may be made from polycarbonate sheeting, woven fabric, elastomers, or a combination of materials. A pressure relief device may be rectangular, round, trapezoidal, triangular, or any custom shape desired to fit a given application.
A pressure relief device may be provided with at least one designed area of weakness, which controls the set pressure and/or at least one location at which the device will vent fluid from the system. A designed area of weakness may be manufactured directly into the material of the pressure relief device. For example, a burst pattern or opening pattern may be cut by laser, mechanical cutting, water jet cutting, or any other suitable method for cutting the pressure relief device. When cut into a burst pattern or opening pattern, the pressure relief device may concentrate pressure on uncut areas between cuts. These areas may constitute the designed areas of weakness. In another example, a designed area of weakness may be formed by way of a score line, shear line, indentation, or any other suitable manufacturing process that weakens part of the pressure relief device.
A designed area of weakness also may comprise a secondary component added to the pressure relief device. For example, when a pressure relief device is cut into a desired opening pattern, it may be provided with at least one activation component affixed to the pressure relief device. The activation component may take the form of a tab or any other component suitable to control the pressure at which a pressure relief device opens. The activation component may be made from a number of suitable materials. For example, it may be desired to provide a light weight plastic, such as polycarbonate, pressure relief device with at least one metal activation component. Such a pressure relief device will vent fluid when the pressure on the device causes the metal activation component(s) to fail.
The designed areas of weakness may also be designed for the pressure relief device to burst or rupture in a particular pattern. A pressure relief device may be designed to burst or rupture peripherally, such that a single “petal” of the explosion vent opens to release fluid. For example, a rectangular pressure relief device may be cut or weakened on three sides, leaving the fourth side to act as a hinge to retain the device's petal when fluid is released. Alternatively, a pressure relief device may be designed to burst or rupture centrally. For example, a rectangular pressure relief device may be cut or weakened along a diagonal line and a circular pressure relief device may be cut or weakened along a radial line.
Pressure relief devices may be provided with activation sensors to detect when a pressure relief device is opened or activated, e.g., in response to an overpressure situation. Such activation sensors are disclosed in commonly owned U.S. Pat. Nos. 4,978,947 and 6,598,454, the entire contents of which are hereby incorporated by reference. An activation sensor may be a magnetically activated proximity switch. Alternatively, an activation sensor may be a loop of wire that breaks when the pressure relief device opens. Such activation sensors may be used to trigger an automated process shut down upon activation of the pressure relief device.
A pressure relief device may become strained or compromised without activation. Sources of strain on a pressure relief device may include damage due to external factors such as wind, lightning, or impact by a foreign object. Another source of strain on a pressure relief device may be pressure from the system. For example, a pressure relief device may experience subtle changes in its physical profile as the pressures applied to it—including forward and back pressures—change. A pressure relief device may have a particular region or feature that is particularly responsive to such changes prior to activation of the pressure relief device. That region may occur at or adjacent to a designed area of weakness. Alternatively, that region may occur at a point that is apart from the designed area of weakness but nonetheless experiences a relatively high level of pre-activation deformation in response to pressure changes. As one example, in a pressure relief device having a cross-shaped score line pattern that divides the pressure relief device into four “petals,” a particularly responsive region may be located near the center of each petal. Whether located at a designed area of weakness or elsewhere, a particularly responsive region may be referred to as a pre-activation reactive region.
If a pressure relief device is strained or compromised without activating, the compromised condition may go undetected by an activation sensor. In addition, a strained or compromised pressure relief device may not be detected by visual inspection. Many pressure relief devices are used in remote, concealed, or elevated areas that make visual inspection difficult. Additionally, many pressure relief devices are used in negative pressure systems that would prevent gases or liquids from visibly leaking out of a damaged pressure relief device. Such systems may make the telltale signs of process leakage unavailable or unreliable as a means of identifying the compromised condition of the pressure relief device.
An undetected leak can be dangerous or otherwise undesirable, because it may vent gas or liquid from the system into the environment. Additionally, an undetected leak may expose the system to undesirable elements from the environment, such as moisture, gas, or dust ingress from the surrounding environment. An undetected strain on the pressure relief device may adversely affect the performance of the pressure relief device, including its longevity or the pressure at which it will activate.
In light of the foregoing, there is a need for a pressure relief device integrity sensor that can detect an abnormal mode of a pressure relief device—i.e., when a pressure relief device has become compromised or strained without activating, or when activation of a pressure relief device is imminent but has not yet occurred. Thereby, an operator may know to replace a compromised or strained pressure relief device before secondary complications or dangers occur. The integrity sensor—and associated systems and methods—of the present disclosure achieves these, or other, advantages.